The present invention relates to a signal processing apparatus for reducing the fluctuation of an image by the fluctuation of a video camera.
A conventional method of reducing the fluctuation of an image due to the fluctuation of a video camera is disclosed in JP-A-61-237581. FIG. 7 shows a block diagram for such a method. A signal from a video camera is converted into a digital signal and a motion vector is obtained on a frame image unit basis by using a frame memory and a correlator. An area to read out the image is determined by a stabilizing signal generator by using the motion vector. As a method of deciding the area, it is obtained from the difference between the movement amount of the image which was obtained by integrating the motion vector and a reference line which was obtained by smoothing the movement amount. The area is determined by using the above method, the image signal is read out of the frame memory, and the image corresponding to the area determined is output by a stabilizer, thereby reducing the fluctuation of the image.
However, the above method is equivalent to that in which the fluctuation of the image is reduced by the signal in which the low frequency components of the movement amount were eliminated by a simple HPF from the movement amount of the image which had been obtained by integrating the motion vector.
Therefore, in the case where the input image is slowly fluctuating at a low frequency, it is difficult to stabilize the fluctuation by the above fluctuation correcting method. Particularly, if the fluctuation frequency is low, the fluctuation signal obtained by passing through the HPF is set to zero, so that there is a problem such that the fluctuation is never stabilized. On the other hand, when the cut-off frequency of the HPF is set to a low frequency, there is a problem such that a large stabilization range is necessary. In consideration of the above problems, it is an object of the present invention to provide a fluctuation stabilizing apparatus in which even when the fluctuating frequency is low, the fluctuation is sufficiently stabilized and even when the stabilized range is physically narrow, an effective enough stabilization range is obtained.